When you see the error "0x80070570 can't access files" on install click --> Cancel ---> you will be returned to the "Install Now" startup screen and - WITHOUT REBOOTING - just re-start the install.
Now saying that might be a workaround you can try there are a few others. But most wont work as you are only using 1 stick of ram. This is a common windows 7 problem and is posted all over the internet some have found by using only one stick of ram at 2 gig or less has solved it.
Here are a few quotes i found.
"Got this messge repeatedly while trying to do a clean install on my ThinkPad T-61. Reading this forum suggested a RAM problem, so I removed 1-2GB RAM chip from the machine, leaving 1-2GB chip installed. Windows 7 loaded flawlessly after that. Thank you folks so much! "
"I had this problem too all I needed to do was keep trying to install. It keeps loading a little more each time and finally works "
"When I had the 0x80070570, I managed to get through the expanding windows files by changing the harddrive mode from AHCI to IDE. I don't know why this works, but you should try it. Needless to say, I was greatly relieved. Only now I'm stuck at the reboot problem. Lovely. "